The present invention relates to improvements in a power transmission device which is able to absorb axial impact energy and is applicable to a drive shaft and a steering column of an automotive vehicle.
A Japanese Patent Provisional Publication No. 53-91236 discloses a power transmission device arranged to connect a shaft and a pipe by means of a spline coupling so as to allow a relative slide in the axial direction therebetween and to forbid a relative rotation therebetween. Further, a shear pin is installed in a through-hole of the shaft and a through-hole of the pipe to connect the shaft and the pipe so as to restrict the axial movement therebetween. If the power transmission device receives an axial impact applied to the shaft and the pipe, the axial impact energy is absorbed by the axial movement between the shaft and the pipe while absorbing the energy by means of the friction caused by the spline coupling and of a breakage of the shear pin. In case that a universal joint is fixedly installed to an end portion of the shaft by means of a press-fitting, it is necessary to apply a press-fitting force to the shaft and the pipe. If such an installation of the universal joint is simply carried out, the shaft will slide with respect to the pipe through the spline coupling. Therefore, in case of such a conventional power transmission device with a universal joint, it is necessary that the universal joint is installed to the shaft by fixedly supporting an intermediate portion of the shaft by means of a chucking device in order to receive the press-fitting force of the universal joint.